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I am looking for a circuit that can translate phase difference of two sinusoidal signals (operating at ~1MHz) to analog voltage swing of 0 - 5V.

The signal A & B comes from the capacitors of two different RLC circuits.The conditioning circuit should not load the circuit as it will change the RLC filter circuit operating point.

I could think about digitizing sine signal + EXOR + filtering but, the RLC capacitor that I am using is about 50pF and using MOSFET for digitizing didnt help as gate input capacitance did change the operating point of the previous stage.

Another option, I was thinking is using a voltage follower opamp + EXOR + filter and I am looking for opamps that can have inputs > 20V with supply voltage of 5V and operating at >1MHz. Any ideas?

Additionally, I came across CD4046B, but I believe that it also needs digitizing before it is fed into the signal & comparator Inputs.

Thanks in advance!

enter image description here

EDIT1:

Below is a rudimentary circuit (Please ignore part numbers). If the loading is limited to a few 10uAs, then I beleive the operating point would not shift that much.

enter image description here

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    \$\begingroup\$ Please provide a complete circuit with the RLC's \$\endgroup\$
    – Voltage Spike ♦
    Commented Sep 30, 2019 at 15:35
  • \$\begingroup\$ XOR gate is simple with buffered signals. then LPF gives DC. But not bipolar in phase with voltage, so show impedance specs of all expected interface signals and purpose. 20~30V sounds like an IAPS \$\endgroup\$
    – D.A.S.
    Commented Sep 30, 2019 at 15:41
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    \$\begingroup\$ It's impossible to measure a circuit without loading it somehow; what amount of loading is tolerable? \$\endgroup\$
    – Hearth
    Commented Sep 30, 2019 at 15:45
  • \$\begingroup\$ Is this homework? \$\endgroup\$
    – winny
    Commented Sep 30, 2019 at 15:48
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    \$\begingroup\$ The 4046 will take fractional-volt analogue signals into the comparator. \$\endgroup\$
    – Andy aka
    Commented Sep 30, 2019 at 17:26

1 Answer 1

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schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Yes Indeed. Thanks :) \$\endgroup\$
    – JSr
    Commented Oct 1, 2019 at 15:40

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